How to Make It
Heat 1 1/2 teaspoons oil in a large nonstick skillet over medium. Add onion and garlic; sauté 3 minutes. Place onion mixture, oats, 1 tablespoon vinegar, 3/4 teaspoon salt, pepper, eggs, and lentils in a food processor; pulse 3 to 4 times. Shape mixture into 12 patties.
Heat 1 1/2 teaspoons oil in pan over medium-high. Add 6 patties to pan; cook 2 minutes on each side. Remove from pan. Repeat with 1 1/2 teaspoons oil and remaining 6 patties.
Combine remaining 1 tablespoon vinegar and remaining 1 tablespoon oil in a large bowl, stirring with a whisk. Add arugula and spinach; toss.
Combine remaining 1/4 teaspoon salt, yogurt, juice, and mint in a bowl. Divide arugula mixture among 4 plates; top each serving with 3 patties and 2 tablespoons yogurt mixture. Sprinkle evenly with pistachios.