Preheat the oven to 425°F (220°C) and line a large sheet pan with parchment paper.

Prep vegetables (for sandwich): Cut zucchini, eggplant, onion, and bell pepper into strips or wedges. Place on one side of the sheet pan. Drizzle with 2 tablespoon olive oil, sprinkle with oregano, salt, and pepper, and toss to coat.

Add garlic (for sauce): Slice the tops off two garlic heads, drizzle with 1 tablespoon olive oil, and wrap loosely in foil. Place on the same pan as the vegetables.

Roast everything together for 25-35 minutes, flipping vegetables halfway through, until tender and lightly browned. The garlic will likely need a full 35-40 minutes, remove vegetables as they finish and let the garlic continue roasting until soft and golden.

Prep sauce ingredients (for sauce): While the vegetables and garlic roast, measure and prepare the remaining sauce ingredients (beans, herbs, lemon juice, salt) so they're ready to blend once the garlic is done.

Make the Garlic Herb Sauce (for sauce): When the garlic is cool enough to handle, squeeze the cloves into a food processor. Add beans, remaining 1 tablespoon olive oil, lemon juice, salt, and herbs. Blend until smooth, adding 1 tablespoon water if needed to loosen. (If skipping the sauce, use your favorite store-bought or homemade herb spread instead.)

Assemble sandwiches (for sandwich): Toast or warm the bread if desired. Spread the Garlic Herb Sauce (or alternate spread) on both sides of the bread, layer roasted vegetables evenly, top with microgreens or arugula, and close the sandwich.

Serve: Slice in half and enjoy warm or at room temperature.