Heat grill to medium (350° to 450°). Rub steaks with 1 1/2 tsp. oil total and season with 1/2 tsp. salt and 1/4 tsp. pepper. Grill meat, turning once, until medium-rare, 8 to 9 minutes. Let rest about 5 minutes.
Combine remaining 6 1/2 tbsp. oil and 3/4 tsp. each salt and pepper, the lemon zest and juice, garlic, and mint in a bowl. Spoon 2 tbsp. dressing into another bowl.
Thinly slice steak crosswise and toss with the 2 tbsp. dressing.
Arrange mâche, cucumbers, feta, and pea pods on plates in a fluffy mound. Tuck steak into layers of salad. Serve immediately with remaining dressing.