Step 1

Heat oil in a small saucepan over medium-high. Add onion, garlic, and thyme; season with salt. Cook until onion is translucent, about 3 minutes. Add orange concentrate and brown sugar. Bring to a boil, then cook until syrupy and reduced to a scant 1 cup, 8 to 10 minutes. Add vinegar and jalapeños; cook 1 minute. Let cool 10 minutes. Set aside 1/4 cup glaze for serving.

Step 2

If using wooden skewers, first soak in water 30 minutes, then drain (to prevent burning). Lay 6 shrimp side by side; slide a skewer through head ends to secure together. Thread a second skewer through tail ends. Spread shrimp slightly so there are small gaps between them. Repeat with remaining shrimp.

Step 3

Preheat grill to high; brush grates with oil. Grill bread, flipping once, just until lightly charred and crisp in places, 1 to 2 minutes total. Transfer to a platter or board; brush with oil.

Step 4

Brush shrimp with half of remaining glaze and grill, turning once, until opaque and almost cooked through, about 3 minutes. Brush with more glaze, turning a few times to caramelize, until just cooked through, about 1 minute more. Remove from grill and brush with some of reserved glaze. Serve over grilled bread, with remaining reserved glaze on the side.