Cook pasta in a pot of boiling salted water until al dente (about 8-10 minutes). Drain, reserving 1/2 cup of pasta water.
While pasta is cooking, heat oil in a large skillet. Add garlic and cook for about 1 minute. Add grape tomatoes and cook until they are warm, about 3-5 minutes. Remove garlic and tomatoes from heat. Stir in pesto. If needed, add small amount of reserved cooking water until proper consistency is achieved.
Serve sauce over individual plates of pasta. Garnish with fresh basil and freshly grated Parmesan, if desired.