Line a large rimmed baking pan with paper towels; spread thawed sweet corn blend in prepared baking pan. Pat dry with additional paper towels. Finely chop ½ red onion; slice remaining half and set aside.

Spray a large nonstick skillet with nonstick spray. Add chopped onion and cook over medium heat for 2 to 3 minutes. Add garlic and cook for 1 to 2 minutes or until fragrant. Stir in sweet corn blend and cook for 2 to 3 minutes or until softened.

Transfer half of the sweet corn mixture to a food processor. Add ½ package feta cheese, bread crumbs, 1 tablespoon cumin, mustard, Worcestershire, black pepper, cayenne pepper, and egg. Cover and pulse until combined. Stir in remaining sweet corn mixture and 7 grains blend.

Press mixture into 8 (¾-inch-thick) patties, using about ½ cup for each. Wipe skillet clean with paper towels. Heat vegetable oil in skillet over medium-high heat. Cook burgers in 2 batches for 8 to 10 minutes or until browned (165°), turning once halfway through.

Stir together mayonnaise and remaining 2 teaspoons cumin; spread on bun tops. Slice remaining ½ package feta. Top bun bottoms with arugula, burgers, sliced feta, sliced red onion, and avocados. Sandwich with remaining bun tops.