Bring a large pot of salted water to a boil. Add the pasta and cook according to the package directions until al dente. Reserve 1 cup of pasta water and then drain and set aside.
While the pasta is cooking, place a large skillet over medium heat. Once the oil is hot add the red onion and cook for 3 minutes, stirring occasionally.
Add the sliced bell peppers to the skillet and cook for 2-3 minutes. Add the zucchini and cook for another 2 minutes.
Add the garlic, Italian seasoning, and salt to the veggies. Cook for 1 minute until fragrant.
Mix the drained pasta with the veggies in the skillet and drizzle with lemon juice. (If you want the pasta to be creamier, add splashes of pasta water to the skillet and stir until your desired consistency is reached.)
Serve warm, garnished with parmesan and chopped parsley if desired.
Notes
If you want to add some protein to this pasta, top each portion with sliced grilled chicken breast or cooked shrimp.
To make this dish vegan, skip the parmesan cheese.