In a food processor or blender, combine coconut milk, lime juice, onion, cilantro, salt and jalapeno pepper. Process until smooth.
Place chicken thighs in a large bowl or any container that can be covered. Pour marinade over chicken, stir with tongs, cover and refrigerate for at least 1 hour or overnight (but no more than 24 hours).
Preheat grill on medium-high heat (400-450F) and rub grill grates with oiled paper towel. Place chicken thighs skin side down on the grill, close the lid and cook bone-in chicken thighs for 7-8 minutes, boneless chicken thighs for 5-6 minutes. Turn the chicken over, close the lid and cook for another 7-8 minutes or 5-6 minutes or until internal read thermometer inserted in the thickest part has reached 165 degrees F.
Remove chicken on a platter, cover with foil and let rest for 5 minutes.
Store: Refrigerate covered for up to 5 days. Freeze for up to 3 months.
Reheat: In a skillet, add a splash of water or broth and grilled chicken thighs. Simmer covered on low for 5 minutes.
Make ahead: Chicken can be marinated for a maximum of 24 hours.
Some chicken thighs are larger and contain more fat than others. Also some grills run hotter. If you see your chicken thighs on the grill are causing too many flare ups, use two zone grilling method. Keep burners on one side and move chicken to the other side and grill over indirect heat.