Here goes:
1 med onion
1 red pepper
(1 green pepper if you like it, but I think it gets too bitter)
1 lg or 2-3 roma tomatoes
3-4 cloves of garlic
handful of cilantro
1 - 1.25 lb white fish fillets , cut crosswise into 3-4 inch pieces
Mince in a food processor until fine, but still with some texture. You could finely dice by hand if you prefer.
In a large skillet on med high, heat a small glug of olive oil, then add onion mixture. Add cumin, chili powder, salt and pepper to taste. (My dh likes crushed red pepper, too.) Bring to a simmer, add fish and cook until it flakes easily, usually just a few minutes. You can serve over rice or potatoes, or even mashed cauliflower or bread.
Canned tomatoes work, even ro-tel with the chile peppers.
Some recipes for soffrito out there use a mix of red and green peppers, some all green. You can use whatever you like or have on hand. Most don't include the tomato, or in smaller amounts. I generally use 2 parts pepper to 1 part onion to 1 - 2 parts tomatoes. (We like it saucy.)
This recipe for Salon Cakes works nicely. I forgot the egg once and nobody noticed it, so I just leave it out now and sub flax meal or something similar for the bread crumbs. GF crackers would work, almond meal. Lots of stuff. I've used all sorts of things based on what I have in the cabinet. And in general I use two small (7 oz) cans of salmon to one small can of anchovies.