In a large bowl, combine the chicken thighs with the peri-peri marinade and ensure even coating; allow to marinate for at least 30 minutes if time permits.
Preheat a cast-iron griddle pan or outdoor grill to medium-high heat.
Place the marinated chicken on the grill and cook for approximately 6 to 8 minutes per side, ensuring the internal temperature reaches 75C (165F).
While the chicken is grilling, bring a medium saucepan of salted water to a boil.
Add the frozen peas to the boiling water and cook for 3 minutes; drain thoroughly.
Return the peas to the saucepan and add the butter, minced chili, mint, and lemon juice; use a fork or potato masher to lightly crush the peas while mixing the ingredients.
Heat a separate non-stick skillet over medium-high heat with the olive oil.
Pat the halloumi slices dry and sear them in the skillet for 1 to 2 minutes per side until a golden-brown crust forms.
Plate the grilled chicken alongside the seared halloumi slices and the chilli mint peas, serving immediately.