Lamb Sliders with Feta Cheese, Red Onions, and Cumin Mayonnaise

INGREDIENTS

• olive oil, as needed
• 1 pound ground lamb
• 1/2 cup mayonnaise
• 6 thick slices Greek feta cheese
• red onion, thinly slice, to taste
• 6 mini or "slider" buns
• salt and freshly ground pepper
• 2 teaspoons ground cumin, more or less, to taste