Active Time

　　50 minutes

　　Total Time

　　1 hour, 10 minutes

　　Bright zucchini, sweet corn, nutty millet, and creamy white beans add vibrant flavor and texture to these hearty, grill-able vegetarian burgers. Bonus: they're gluten-free!

　　

Ingredients

4 servings

　　1 large onion

　　1 garlic clove, coarsely chopped

　　1/2 cup cornmeal

　　1 1/2 cups (packed) coarsely grated zucchini (from about 1 medium zucchini), squeezed to remove excess water, divided

　　1/3 cup white beans, rinsed, divided

　　1/4 cup frozen corn (preferably fire-roasted) , thawed, divided

　　2 tablespoons vegetable oil, divided, plus more for brushing

　　3/4 cup cooked millet or white quinoa

　　1/2 cup finely chopped basil, divided

　　1 teaspoon kosher salt, divided

　　1 teaspoon freshly ground black pepper, divided

　　1/3 cup mayonnaise

　　1 1/2 teaspoons finely grated lime zest

　　1 1/2 teaspoons fresh lime juice

　　4 slices white cheddar

　　4 hamburger buns

　　Green leaf lettuce, (for serving)

　　1 avocado, cubed, lightly smashed

　　

Step 1

Cut onion in half crosswise. Slice one-half into 1/4" rings; set aside. Finely chop remaining onion. Pulse chopped onion, garlic, cornmeal, 3/4 cup zucchini, 2 Tbsp. beans, and 2 Tbsp. corn in a food processor until finely chopped, 30–45 seconds.

　　

Step 2

Heat 1 Tbsp. oil in a large skillet over medium. Add chopped onion mixture and cook, stirring occasionally, until mixture begins to soften and thicken, 3–4 minutes. Add remaining 3/4 cup zucchini and cook, stirring occasionally, until zucchini begins to soften and become translucent, 3–4 minutes more.

　　

Step 3

Transfer mixture to a large bowl and gently mix in millet, 1/4 cup basil, 3/4 tsp. salt, 3/4 tsp. pepper, and the remaining beans and corn until well combined. Form mixture into 4 (1"-thick) patties. Cover with plastic and freeze 20 minutes.

　　

Step 4

Meanwhile, combine mayonnaise, lime zest, lime juice, and remaining 1/4 cup basil in a small bowl; set aside.

　　

Step 5

Prepare a grill for medium-high heat or heat a grill pan or cast-iron skillet over medium-high; oil grate or pan. Toss reserved onion rings with 1 Tbsp. oil and remaining 1/4 tsp. salt and 1/4 tsp. pepper. Cook onion rings until softened and lightly charred, about 5 minutes.

　　

Step 6

Brush patties all over with oil. Cook, flipping once, until medium brown and toasted, about 7 minutes on each side; add 1 slice cheese to each during last 3 minutes of cooking. Transfer onions and burgers to a plate. Toast buns until golden brown, about 30 seconds.

　　

Step 7

Place 1 piece lettuce on each bottom bun and top with a burger. Top with onions. Spread 1 Tbsp. basil mayonnaise on each top bun, add smashed avocado, and close sandwiches.

　　Cooks' Note

　　Burgers can be made 3 months ahead; tightly cover and freeze. To serve, cook frozen patties 10 minutes on each side, adding cheese during last 3 minutes of cooking.