Preheat a grill or oven to 450 degrees F. If using a grill, set up hot and cool zones by turning one side of a gas grill to the high setting or by banking very hot coals on one side of a charcoal grill.
Whisk together the maple syrup, mustard and soy sauce in a medium bowl. Toss the chicken in the marinade and season with salt and pepper. Place the chicken on the hot side of the grill bone-side down and grill 3 to 5 minutes. Move the chicken to the cool side of the grill, close the lid and cook until the thickest part of a thigh registers 160 degrees F, 30 to 40 minutes. If using the oven, place the chicken bone-side down on a sheet tray and roast until the thickest part of a thigh registers 160 degrees F, 30 to 40 minutes.
Meanwhile, add the bacon to a large saucepan over medium heat and cook, stirring occasionally, until crispy, 5 to 6 minutes. Add the greens, chile flakes if using, a pinch of salt and 1/4 cup water and cover with the lid. Cook until the greens are tender, about 5 minutes. Splash with some vinegar and serve with the chicken on top.
For more ingredient substitution ideas, see the article below.