Grilled Tuna Sandwich with Lemon-Chili Mayo for Two

Preheat grill to medium-high.

Lightly brush both sides of bread slices with oil. Brush tuna with the remaining oil and sprinkle with 1/4 teaspoon chili powder and salt.

Grill the tuna, turning once, until cooked through, 4 to 6 minutes per side. Transfer to a clean cutting board. Grill the bread, turning once, until beginning to brown, about 1 minute per side.

Combine mayonnaise, lemon zest, lemon juice and the remaining 1 1/2 teaspoons chili powder in a small bowl. Thinly slice the tuna with the grain.

To assemble the sandwiches, divide the lemon-chili mayonnaise between 2 slices of bread (about 2 tablespoons each). Top with about 3/4 cup watercress (or arugula), the tuna and the remaining slices of bread.