Bring a large pot of water to boil for the pasta. Once boiling, add some salt and undercook the pasta, about 7 minutes, until just under al dente.
Pre-heat broiler and set rack 12 inches from heat.
While the pasta cooks, heat 1 tablespoon EVOO in a large, deep, nonstick skillet over medium-high heat. Add the chopped bacon and cook till golden and crispy. Remove with a slotted spoon to a paper towel-lined plate and reserve.
Add another tablespoon EVOO to the skillet, one turn of the pan. Add onion and cook till soft, 4-5 minutes. Add flour and cook another 1-2 minutes before adding the chicken broth – it should look real pasty and thick. Whisk in milk and bring to a bubble, season with salt and pepper, and stir in the mustard. Lower heat and add 1 1/2 cups of each cheese. Stir to melt, 1 minute. Adjust seasoning with mustard, salt and pepper, to your taste.
Drain pasta well. Combine pasta, zucchini, red bell pepper and peas with the cheese sauce to warm through, stir in chopped parsley, then pour into large casserole and top with remaining cheese.
Transfer to broiler to melt and brown cheese, about 2 minutes, and serve.