Prepare grill for direct-heat cooking over medium heat.
Gently mix pork, chipotle, garlic, and a scant teaspoon salt until just combined. Form into 4 (1/2 inch thick) patties.
Oil grill rack, then grill patties, covered for 4 minutes.
Flip patties and top with a slice of cheese. Grill, covered, until just cooked through, 1-2 minutes more.
Spread buns with mayonnaise and assemble burgers with tomatillo, avocado and cilantro.
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