I've made several dozen versions of this basic dish over the past few months. Cooking's all about iteration. Forget the recipe, forget technique, forget ingredient quality. Those vaunted X factors are dwarfed by the magical power of iteration; fine-tuning your moves (and, even more importantly, your micro-moves). The easy informality of it all, combined with absolutely full attention and deep caring, is the trick.
My guiding principle is to be as lazy as I can get away with. Not because I'm lazy, but because I want to focus, and if I'm navigating a fraught obstacle course where every single task is a demanding stressor, my attention gets diluted and I find myself acting more like a harried project manager than a deeply attentive artisan. I know where to invest my care. That's one thing the iterations show you (of course, you need to carefully analyze your results, or else the iterations won't improve on each other).
The caring part has to be way more extreme than you'd ever imagine. That's why you're lazy; to clear space for excessive caring. Not a cinematic display of furrowed brow where you tell yourself stories about your own diligence. Don't pose, but really do it. Lose yourself in it. Cook like you're saving a life.
See the religious tract I once posted about the devotional level necessary for producing a properly toasted and buttered bagel.
Ok, here goes.
Have some leftover salmon that was broiled first flesh side up and then skin side up until the skin nearly burnt. The skin won't remain crispy in the fridge, but you'll be rejuvenating it.
Heat water in a pot (use minimal water so it becomes starchy and thick and useful for adding later to make final results glisten).
Roughly chop a small onion and sauté in minimal oil. Cook it (seasoned with salt/pepper) about two notches cooler and twice as long as you ordinarily would. "Gentle" is your mantra. Stir infrequently (laziness!).
When you start the pasta, add thinly-sliced garlic to the onions (if the pan's actively sizzling, you'll brown or burn the garlic, so be sure the heat's tame before you add).
Roughly chop salmon and place atop the onion/garlic mixture. You don't want to use a ton of salmon. One full handful, roughly chopped, is sufficient per person. Don't do the ugly American move of deeming your protein the equivalent of a steak dinner. Be poor tonight.
Cut the salmon skin into small strips with paring knife, and add to sauté pan, keeping it separate from the other items.
Slice some tomatoes (I used Camparis) and place above the salmon which sits atop the onion/garlic. You don't want to cook the tomatoes to mushiness.
Drain pasta, saving water.
Hastily sauté a handful of spinach per serving in a little too much olive oil in the pasta pot (excess oil will help compose the sauce).
Critical checks before proceeding:
Salmon skin must be dry and crisp - almost starting to curl up.
Onions and garlic must be soft and golden.
Tomatoes must be relaxed but not gooey.
Spinach must be limp but still deeply green.
Remove salmon skin from pan, and keep handy on a plate.
Mix salmon, onions, and garlic.
The following should take about 30 seconds:
Add cooked pasta to pot with spinach, hoist the pot with one hand and stir aggressively and disrespectfully with the other hand, using a wooden or bamboo spoon or spatula.
Add a dab of cooking water.
Add salmon/onions/garlic/tomato (don't stop stirring!).
Add a dab of cooking water.
Stir in some seasoning (I used leftover Ecuadorian creamy hot sauce from a previous day's takeout, but sky's the limit: chili flakes, za'atar, any fresh herbs, etc.).
Add a dab of cooking water.
Add some grated Parmesan (not too much; this needs to be subliminal; cheese is great with salmon, but you don't want to flaunt the broken taboo).
Keep stirring violently until it looks like something you'd be eager to eat.
Transfer to plate.
If you're using lengthy pasta (linguini, spaghetti, etc), use tongs and give the mound a twist as you plate it. Carefully study 2'29" in this classic short video for spaghetti limone, where Frank Prisinzano makes that move look way too easy.
Arrange salmon skin atop.
Walla.
Read this followup posting more closely explaining about the onions.