Step 1Toss the zucchini, yellow squash, red bell pepper, orange bell pepper, onion and tomatoes with the olive oil and sprinkle with salt and pepper. Grill on a grill screen over medium fire, covered, until browned and tender, 5 minutes on a side.
Step 2Put a medium skillet over high heat. Add the butter and cook until it begins to brown lightly . Remove from the heat and stir in the vinegar and capers.
Step 3Cut the vegetables in large bite-sized chunks, put in a serving bowl and pour the warm brown-butter vinaigrette over the vegetables. Serve immediately.