Place the chicken breast-side down and cut along both sides of the backbone to remove it. Flip and press down on the breastbone until the bird lies flat.
Cut 1-inch deep slits into the thickest parts of the breasts and thighs.
In a blender, combine the oil, red pepper, chilies, vinegar, garlic, paprika, bay leaf, oregano, and salt. Blend for 2 minutes until smooth.
Pour the sauce into a saucepan, add the butter, and heat over medium until butter melts. Simmer for 1 minute, remove from heat, and stir in the lemon juice.
Set up the grill for two-zone cooking with one side high heat (450-500F) and the other low.
Season the chicken generously with the salt on all sides.
Place the chicken skin-side down on the hot side and sear for 4 minutes until grill marks appear.
Flip the chicken and move to the cooler side, skin-side up. Brush generously with the piri piri sauce and cover.
Continue flipping and brushing with sauce every 5-7 minutes until the chicken reaches 165F at the thickest part (35-45 minutes total).
Let rest for 10 minutes before carving.