Brush lemon juice over halibut fillets. Sprinkle with minced ginger, 1/4 teaspoon salt and pepper.
Place fish on an oiled grill rack, skin side down. Grill, covered, over medium heat (or broil 6 in. from heat) until fish just begins to flake easily with a fork, 6-8 minutes.
In a large skillet, bring water to a boil over medium-high heat. Add Brussels sprouts, pepper flakes and, if desired, remaining salt. Cook, covered, until tender, 5-7 minutes. Meanwhile, in a small skillet, heat oil over medium heat. Add garlic; cook until golden brown. Drain on paper towels.
Drizzle sesame oil and soy sauce over halibut. Serve with Brussels sprouts; sprinkle with fried garlic. If desired, serve with lemon slices.
