In a food processor, purée egg, mushrooms, onion, garlic, mint and oregano. Add salt and pepper to taste. Add lentils and bread crumbs; pulse until incorporated. Shape into 4 patties, each 1 in. thick.
In a large non-stick skillet, heat 2 tsp (10 mL) of the oil over medium-high heat; fry eggplant, turning once, until tender and golden, about 5 minutes. Remove to plate.
Reduce heat to medium; add remaining oil to pan. Fry patties, turning once, until crusty and browned, about 12 minutes.
Sandwich lettuce, patties, eggplant, tomatoes and cucumbers in buns, along with the burger condiments of your choice including goat cheese, if desired.
Per serving: 449 calories, 22 g protein, 8 g fat (1 g saturated fat), 75 g carbohydrates, 15 g fibre, 53 mg cholesterol, 342 mg sodium.