If using wooden skewers, soak them in water for at least 30 minutes to prevent them from burning on the grill. Heat the grill to medium.
Cut the stems off the Brussels sprouts, and remove any yellow outer leaves. Cut really big ones in half, aiming to have all the sprouts at roughly the same size.
In a large mixing bowl, whisk together the olive oil, garlic powder, mustard, paprika, salt, and pepper. Toss the Brussels sprouts in this mix, adding a touch more olive oil if needed.
Fit 4 to 5 Brussels sprouts onto each skewer, leaving about a half inch between them. If there's any leftover seasoning mix, brush that over the skewers.
Grill for 3 to 5 minutes, then quarter-turn them. Repeat four times until all sides are nicely charred.
Squeeze some lemon juice over the cooked sprouts, and top with freshly ground pepper.