Slice the ends off two to three zucchinis. Use a vegetable peeler to shave off strips of zucchini. It's easier than you think it'll be.
Add the tomatoes and heat until the sauce begins to simmer. Lower heat and cook (uncovered) until thickened, about 15 minutes. Stir frequently.
Preheat the oven to 400 degrees Fahrenheit. In a large pan, heat the oil over medium heat. Add the onions and garlic and sauté until the onion starts to caramelize, which will take about 10 minutes. Add the pepper flakes and red pepper and cook until the pepper softens, about 2 minutes.