Cook your pasta (by the time it's done, your sauce will be ready). Pour the olive oil into a pan over medium-high heat, and then in go the chili pepper flakes, if using, garlic and zucchini. Saute 1 minute, keeping an eye on the zucchini so it doesn't burn. Add the cherry tomatoes and some salt and cook until the zucchini and tomatoes soften.
Toss the spaghetti in the pan with the vegetables. Remove from the heat and stir in the shrimp (the steam from the pasta will cook the delicate shrimp quickly). Finish with the parsley and a drizzle of olive oil.