Combine garlic, lemon juice, olive oil, and pepper in a gallon freezer bag. Add steak to the bag and let marinate in the refrigerator 30 minutes-2 hours.
Bring steak to room temperature by removing from refrigerator 15-30 minutes prior to cooking. Remove from marinade and pat dry. Set an oven rack 4-5 inches from broiler heating element and preheat broiler to high.
Heat a small skillet over high heat. Add steak and sear 2-3 minutes per side, using tongs to flip in between. Place skillet in oven under broiler and broil on each side 2-3 minutes, again using tongs to flip.
Carefully tent aluminum foil over skillet and let steak rest while you prepare the rest of the salad.
Make the salad:
In a large bowl, toss chopped red cabbage, chopped romaine, red peppers, feta, and cannellini beans.
Make the dressing:
In a 1-cup measuring cup, combine all ingredients. Using an immersion blender, mix until emulsified.
Put it all together:
Slice steak into cubes, cutting against the grain, and add to salad. Serve with dressing on the side.