Roast onions or bell peppers in 1 tbsp oil for 2 mins. Transfer to a plate to cool.
Roast tomatoes until mushy for about 3 mins. Cool this as well.
Blend them together to a puree. Set aside
In a large pot, bring water to a boil. Cook pasta with salt until al dente
Drain off and rinse them. Drain in a colander. Set aside.
Heat the same pan with more oil and fry garlic and chili flakes until aromatic.Add onions and saute until golden
Pour the puree and add salt. Mix well and cook until it reaches a desired consistency. Make sure the sauce is not watery. Taste the sauce and adjust salt as needed. Add oregano.
Off the stove and add the pasta. Toss well until mixed. Serve hot.