In a large pot fitted with a steamer basket, bring about 1 inch of water to boil. Add the broccoli, mushrooms, zucchini and peppers. Cover and steam until tender-crisp, about 10 minutes. Remove from the pot.
In large saucepan, heat the olive oil and saute the onion and garlic over medium heat. Add the steamed vegetables and stir or shake to coat the vegetables with the onion and garlic mixture. Remove from heat but keep warm.
In another large saucepan, heat the butter, evaporated milk and Parmesan cheese. Stir over moderate heat until somewhat thickened and heated through. Stir continuously and don't scald. Remove from heat but keep warm.
In the meantime, fill a large pot 3/4 full with water and bring to a boil. Add the pasta and cook until al dente (tender), about 10 to 12 minutes, or according to package directions. Drain the pasta thoroughly.
Divide the pasta evenly among individual plates. Top with vegetables and pour the sauce over the vegetables and pasta. Garnish with fresh parsley and serve immediately.