1. In a small bowl, mix together all the mayo ingredients (well combined), then refrigerate while you prepare the rest of the sandwich.
2. Preheat a grill to medium-high.
3. In a large bowl, toss together the eggplant, zucchini, yellow squash, pepper, and onion.
4. Drizzle with 2 tablespoons olive oil and the oregano. Toss to coat. Transfer to a grill basket.
5. Brush both sides of the mushroom caps with an additional tablespoon of olive oil. Season with salt and pepper.
6. Place the grill basket and the mushroom caps on the preheated grill. Cook the mushrooms for 4-5 minutes, until they begin to release their moisture, then flip and cook an additional 3-4 minutes. Remove from the grill and slice thinly.
7. Stir the veggies frequently and grill until they are tender, about 10 minutes. If you have any larger pieces, you may wish to remove them from the basket and cook them directly on the grill. Once tender, remove from grill.
8. If using sliced bread, brush both sides of the bread with the remaining olive oil (if using a bun only brush the inside), grill each slice for a minute on each side until just toasted. Remove from grill.
9. To assemble the sandwiches, spread the mayo on your toasted sliced bread or bun. Layer with a single layer of each veggie. Spread mayo on another slice and place on top.

Optional: add any of your favorite fresh veggies.

*Recipe courtesy of Great Lakes Greenhouses