Put a pot of water on to boil.
In a large skillet over medium-high heat, cook the onion in 3 tablespoons olive oil until softened, 5 to 8 minutes. Reduce heat as necessary to keep onions from browning.
Add zucchini, season generously with salt and pepper, and continue cooking, stirring occasionally until it softens, about 10 minutes. Turn off heat.
Meanwhile, in a food processor pulse garlic, basil and a little salt until it looks a bit like paste. Add mixture to small bowl and stir in 3 tablespoons olive oil.
Cook pasta according to directions.
For perfectly al dente pasta cook it for 3 minutes less than the cooking time on the package. Use a measuring cup to get about a cup of pasta water, then drained cooked pasta.
Add cooked pasta to zucchini in skillet and turn heat to medium-high.
Add 1/2 cup cooking water, then the ricotta, crushed red pepper and lemon zest, stirring to distribute.
Check seasoning and adjust. Cook for 1 minute more. Mixture should look nice and creamy.
If the sauce is too thick, add a little more pasta water, 1 tablespoon at a time, to loosen it up.
Add the basil mixture and half the grated cheese and quickly stir to incorporate.
Divide pasta among 4 bowls and sprinkle with more cheese -- because you can never have too much cheese on your pasta!