Heat olive oil in a small nonstick saucepan. Add shallots or onions and cook until soft and wilted, not browned (about 2 minutes). Add garlic and stir for 30 seconds. Add pomegranate-blueberry juice, preserves, and vinegar. Increase heat to bring the sauce to a light boil, stirring occasionally. Let the sauce reduce to half the original amount (about 10 minutes). It should get thick and syrupy.
Meanwhile, preheat broiler. Pat steaks dry and sprinkle with little salt and pepper on both sides of steaks. Broil to the desired level of doneness. For medium-rare, cook about 3 minutes per side; for medium, cook about 3½ minutes per side; for medium-well, about 4 minutes per side.
To serve: Divide greens among 4 plates. Top each with a piece of steak. Divide and sprinkle around each some blueberries and pomegranate seeds or strawberries. Drizzle warm sauce all over top of steak and greens. If sauce is too thick, stir in a tablespoon or so of pomegranate-blueberry juice before drizzling. Sprinkle each with 1 tablespoon fat-free feta cheese.