In this menu, guests make their own sandwiches, piling on rosy slices of spring lamb, chopped grilled green onions and a variety of condiments. Uncork a red Rhône wine (we recommend Gigondas) or a Pinot Noir to pour with the sandwiches; have a selection of sodas and bottled water on hand, too.
Using sharp knife, cut 1/2-inch slits all over lamb. Insert garlic slices into slits. Sprinkle lamb with salt and pepper, then herbs, pressing herbs to adhere. (Can be prepared 1 day ahead. Cover and chill.)
Prepare barbecue (medium-high heat). Place green onions in large roasting pan. Drizzle 1/4 cup oil over onions; toss to coat. Sprinkle with salt and pepper. Cut baguette pieces horizontally in half. Brush cut sides of bread with remaining 3 tablespoons oil.
Grill lamb until meat thermometer inserted into thickest part registers 135°F. for medium-rare, turning occasionally, about 30 minutes. Transfer to platter and tent with foil. Let stand 10 minutes.Working in batches, arrange green onions in single layer on grill. Grill until beginning to brown, about 4 minutes per side. Transfer to cutting board. Grill baguettes, cut side down, until golden brown, about 2 minutes.
Chop onions. Place in bowl. Cut lamb diagonally into thin slices. Serve with green onions, baguette pieces, Aioli, Red Bell Pepper Sauce and tapenade.