Tart green tomatillos, which are relatives of tomatoes, cut the sweetness of pineapple in this lively salsa spiked with serrano chiles.
Preheat grill to medium (if using a charcoal grill, coals are ready when you can hold your hand 5 inches above grate for just 5 or 6 seconds). Grill tomatillos, pineapple, and chiles, flipping once, until blackened and cooked through, about 4 minutes per side. Set aside.
Using a mortar and pestle or the side of a large knife on a cutting board, crush together garlic and salt to form a paste. Pulse garlic paste, tomatillos, chiles, and honey in a food processor until coarsely combined; transfer to a bowl.
Cut pineapple into 1/2-inch dice. Add pineapple, cilantro, and onion to the tomatillo mixture; stir until combined. Serve warm or at room temperature.
Salsa can be refrigerated in an airtight container up to 3 days.