Puree garlic, soy sauce, lime juice, olive oil, cumin, paprika, oregano, and black pepper in a blender.
Place chicken thighs in a large ziploc bag and add the marinade. Refrigerate and allow to marinate for 8 to 24 hours.
Make Green Sauce:
Combine jalapeños, cilantro, green onions, garlic, mayonnaise, Greek yogurt, lime juice, salt, and black pepper in a blender. Blend until smooth.
With the blender running, slowly drizzle in the olive oil. Transfer to a bowl and refrigerate until ready to serve.
Grill Chicken:
Preheat grill to medium-high heat (around 350-degrees).
Remove chicken from marinade, shaking off excess. Grill on medium-high for 5-6 minutes per side, covering grill to retain heat. Chicken is done when internal temperature reaches 165°F.