Cook spaghetti until just al dente in salted water. Drain but reserve 1/2 cup pasta cooking water.
Meanwhile preheat oven to 400 degrees F and slice tomatoes. Place them in baking dish with the 1 tbsp oil and seasonings indicated. Toss. Bake until skins are wilting and juices released, around 25 min.
While those are cooking, finely chop the onions and mushrooms and add them to large pan with the 2 tbsp olive oil and the salt, pepper, garlic powder. Cook 10 min on medium, stir occasionally. Add chopped bell pepper, cook another 5 min.
Add garlic, cook another min. Add the roasted tomatoes, the pasta cooking water, tomato paste, crushed tomatoes, chickpeas. Stir well, simmer 3 min.
Add remaining ingredients except spaghetti, toss as spinach wilts then add spaghetti, toss again. Taste for seasoning, serve. Top with more fresh or dried parsley and chili flakes if desired.