Saute 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 the basil.
Slice the potatoes, tomatoes, squash and zucchini in round ¼ inch thick slices. In a large mixing bowl stir together the mustard, balsamic vinegar, salt, pepper,paprika, thyme and oregano. Layer them alternatively in a circular motion on top of the onion mixture. Make sure to fit them in tightly and create a spiral. Bake at 350 covered with foil for 30-40 minutes, remove the foil and bake for another 10-15 minutes.
Recipe by Kitchen Belleicious at https://kitchenbelleicious.com/2012/08/06/colorful-vegetable-tian/