Cook on moderate-high heat until just translucent.
Add cubed corned beef, Brussels sprouts, and onions, and toss until coated. Pour in 1.5 ounces balsamic vinegar and 1 tablespoon lemon juice.
Season with salt and pepper.
Pour mixture into a dish and top with 2 fried quail eggs or one regular chicken egg.
Serve with pickled mustard seeds or other mustard on the side (optional). Pickled mustard seeds: 1/2 cup mustard seeds, 1/2 cup sugar, 1 ounce water. Combine all ingredients and cook on a low temperature until it's all sticky, cool, and serve.