Whisk olive oil, lime juice, cilantro, garlic, mint, lemon juice, and salt in a bowl. Refrigerate salad dressing for at least 1 hour or overnight for best flavor.
Preheat an outdoor grill for high heat and grease the grate.
Toss salad greens, romaine lettuce, mango, peanuts, cucumber, and chow mein noodles in a salad bowl.
Sprinkle tuna with salt and black pepper.
Grill tuna on the preheated grill until the outside is seared and brown and the inside is still red, about 1 1/2 minutes per side for rare. Slice the grilled tuna.
Top salad with slices of avocado and grilled tuna; drizzle with salad dressing to taste.