In a large pot cook penne in boiling salted water until al dente. Drain the pasta, leaving it slightly wet.
While pasta is cooking, wash the capsicums and cut them into 5mm strips. In a large frypan over medium heat place 2 tablespoons of olive oil and saute the capsicums until soft. Do not allow to brown.
To the frypan, add the sliced zucchini and button squash and saute for 2 minutes. Add the sliced mushrooms and minced garlic and saute an additional 2 minutes, stirring frequently. Add the chopped tomatoes and remove from heat.
Serve pasta portions onto warmed plates. Add sauce to top. Sprinkle with salt and pepper to taste.