Step 1: Pin the asparagus stalks crosswise with toothpicks or skewers to make rafts. Pin each onion wedge with a toothpick. Arrange the asparagus, onions, zucchini, squash, Treviso, eggplant slices, and peppers on a baking sheet or grilling grid. Brush the tops with olive oil and sprinkle with dried mint, salt, and pepper. Squeeze a little lemon juice over the veggies. Turn the vegetables over and season the other side the same way.
Step 2: Set up your grill for direct grilling and preheat to high. Brush and oil the grill grate.
Step 3: Arrange the vegetables on the grate and grill until browned, 2 to 5 minutes per side depending on the vegetable. Arrange the grilled vegetables on one side of a large platter.
Step 4: Cut the polenta into 3-inch squares. Lightly brush on both sides with extra virgin olive oil. Grill the polenta until browned on both sides, 3 to 4 minutes per side, giving each a quarter turn after 2 minutes to lay on a crosshatch of grill marks. Arrange the polenta on the other side of the platter.
Step 5: Drizzle more olive oil over the vegetables and polenta and sprinkle with pine nuts. Serve with lemon wedges for squeezing.