How about a brasciole-like filling? Bread crumbs, mozzarella, herbs, prosciutto or pine nuts? raisins?
Horesradish, mayo, a little milk, S&P
Bleu cheese sauce
Here's the recipe in its' entirety. See what you think about the filling:
Sirloin steak flattened and stuffed using the same technique as the classic German beef roulade, but which is adapted for the barbecue.
1½ lb Top Sirloin Grilling Steak or Rouladen-cut Inside Round Marinating Steak
Salt & pepper to taste
4 oz peppered goat cheese (e.g. chevre or feta with black pepper)
2 tsp dried oregano, crumbled
2 cups fresh spinach leaves
12 sun-dried tomatoes (oil-packed)
2 tbsp balsamic vinegar
If using sirloin steak, with mallet, pound steak to 1/8 inch thickness (this step is not necessary if using rouladen-cut steaks). Season beef with salt and pepper. Spread goat cheese to within ¼ inch of each steak’s edge; sprinkle with oregano. Place half of the spinach leaves over cheese. Add sun-dried tomatoes and cover completely with remaining spinach. Starting with long edge, roll up each steak like a jelly roll. Tie tightly in several places with butcher’s twine or hold together with skewers (presoak wooden skewers for 1 hour). Brush outside of each beef roll with balsamic vinegar and olive oil; season with salt and pepper.
Place beef on greased grill over medium heat; close lid and cook, turning once, for approximately 3-5 minutes per side (until instant-read thermometer inserted into center of each roll reads 155°F/68°C). Remove from heat; place seam-side-down on cutting board and tent with foil for 5 minutes. Remove string or skewers and cut diagonally into 1-inch (2.5-cm) slices. Serve the involtini with new potatoes and grilled vegetables tossed in a balsamic vinaigrette.