1. Sauté the onion, garlic and red bell peppers in the olive oil for 5-6 minutes until slightly translucent. Place in the bottom of a round casserole dish or tart pan. Sprinkle with Romano cheese and basil.
2. Slice the potatoes, tomatoes, squash and zucchini in round 1/4 inch thick slices. In a large mixing bowl, stir together the mustard, balsamic vinegar, salt, pepper, paprika, thyme and oregano.
3. Layer them alternatively in a circular motion on top of the onion mixture. Make sure to fit them in tightly and create a spiral.
4. Bake at 350 degrees F covered with foil for 30-40 minutes.
5. Remove the foil and bake for another 10-15 minutes.