Preheat grill to 400° to 450° (high) heat. Cut onion into 1/4-inch-thick slices. Brush with 1 Tbsp. olive oil, and sprinkle with 1/4 tsp. salt and 1/4 tsp. pepper. Cut bell peppers into 1-inch-wide strips. Place pepper strips in a large bowl, and drizzle with 1 Tbsp. olive oil. Sprinkle with remaining 1/4 tsp. salt and 1/4 tsp. pepper; toss to coat.
Grill onion and bell pepper strips, covered with grill lid, over 400° to 450° (high) heat 7 to 10 minutes on each side or until lightly charred and tender.
Brush cut sides of rolls with remaining 2 Tbsp. olive oil, and grill, cut sides down, without grill lid, over 400° to 450° (high) heat 1 to 2 minutes or until lightly browned and toasted.
Spread blue cheese on cut sides of roll bottoms; top with arugula, bell pepper strips, steak, and onion. Spread mayonnaise on cut sides of roll tops. Place roll tops, mayonnaise sides down, on top of onion, pressing lightly.
*French hamburger buns may be substituted. We tested with Publix French Hamburger Buns.
Note: We tested with Saga Classic Soft-Ripened Blue-Veined Cheese.
Flank Steak Sandwiches With Brie: Substitute 5 oz. Brie, rind removed, for blue cheese. Proceed with recipe as directed.
Herb Chicken Sandwiches: Substitute Herb-Marinated Chicken Breasts for flank steak. Proceed with recipe as directed.
Herb Chicken Sandwiches With Grilled Peaches: Reduce onions to 1 and red bell peppers to Cut 2 large peaches into 1/4-inch-thick rounds, cutting through stem and bottom ends. Proceed with recipe as directed, grilling peach slices, covered with grill lid, over 350° to 400° (medium-high) heat 3 to 5 minutes on each side or until grill marks appear. Assemble sandwiches as directed, topping onion with peach slices. Prep: 20 min., Grill: 32 min., Stand: 10 min.