In a large pot of boiling salted water, cook the pasta according to the package instructions until al dente. Reserve 1 cup of pasta water, then drain the pasta and set aside.
In a food processor, combine the avocado, minced garlic, olive oil, lemon juice, basil leaves, and red pepper flakes (if using). Blend until smooth and creamy, adding a little reserved pasta water if needed for a thinner consistency.
In a large mixing bowl, add the drained pasta and the creamy avocado sauce. Toss well to coat the pasta evenly. If the sauce is too thick, gradually add more reserved pasta water until reaching the desired consistency.
Season with salt and pepper to taste. Mix well for uniform flavor.
Divide the pasta among serving plates. Garnish with cherry tomatoes and a sprinkle of grated Parmesan if desired.
Notes
For a thinner sauce, add more reserved pasta water.