In a medium skillet, add the sliced red onions with the olive oil and sugar. Heat the onions on medium high heat for 3-4 minutes, then reduce heat to low and let onions caramelize in the oil and sugar. Cook on low for another 20-25 minutes, stirring often.
Meanwhile, cook the frozen peas as directed. Drain off the hot water and rinse with cold water. Pour into the serving dish and add the crumbled feta. Place in the fridge while the onions finish cooking.
Toss the cooked caramelized red onions with the peas and feta. Chill for at least an hour in the fridge before serving.
Serve Pea, Feta and Red Onion Salad along with your favorite grilled meat and some garlic bread.