1 lb sirloin (about 1 inch thick)
Kosher salt and pepper
3 Tbsp fresh lemon
2 Tbsp olive oil
2 tsp honey
1/2 small red onion, thinly sliced
1 lb cherry tomatoes, halved
1/2 small seedless watermelon
1 c. fresh mint, leaves torn
1 c. fresh flat-leaf parsley leaves
1 small bunch arugula, thick stems discarded
Heat grill to medium-high. Season steak with 1/2 tsp each salt and pepper and grill to desired doneness (six to eight minutes per side for medium-rare). Transfer to a cutting board and let rest before slicing.
Meanwhile, in a bowl, whisk together lemon juice, oil, honey, and a pinch each salt and pepper. Fold in onion and tomatoes.
Cut watermelon into 1/2-inch-thick triangles and cut off rinds. Brush lightly with oil, then grill until lightly charred, one to two minutes per side. Divide among four plates.
Fold herbs into tomato mixture, then gently toss with arugula. Spoon on top of watermelon and serve with steak.