Cook the Pasta: Begin by boiling the pasta in salted water until al dente. Drain, then let it cool slightly.
Prepare the Mushrooms: In a skillet, heat a little olive oil over medium heat. Add the sliced portabella mushrooms and cook until soft and browned (about 5-7 minutes). Set aside to cool.
Make the Pesto Dressing: In a blender or food processor, combine the basil, Parmesan, garlic, pine nuts, olive oil, salt, and pepper. Blend until smooth.
Assemble the Salad: In a large bowl, toss together the cooled pasta, cooked mushrooms, cherry tomatoes, red onion, and pesto dressing until well coated.
Serve and Enjoy: Garnish with extra Parmesan and basil before serving.