Make the rice pilaf: melt 2 tablespoons butter in a medium pot over medium heat. Add the basmati rice, orzo and pine nuts and cook, stirring, until the butter browns slightly and the orzo is lightly toasted, about 2–3 minutes.
Add 2 cups water or broth to the pot and bring to a boil over high heat. Reduce heat to low, cover, and simmer for 10 minutes.
Turn off the heat and let the rice pilaf sit, covered, for 15–20 minutes. Fluff with a fork before serving.
Meanwhile, prepare the chicken marinade: in a mixing bowl combine the chicken pieces, 6 tablespoons melted butter, lemon juice, chopped garlic, smoked paprika, dried oregano, dried rosemary (or thyme), sea salt, black pepper, and chili flakes. Toss until evenly coated. If time allows, refrigerate 10 minutes to overnight.
Preheat a grill, grill pan, or skillet to medium-high. Thread the marinated chicken onto skewers.
Grill the skewers, turning occasionally, until lightly charred and cooked through, about 10–12 minutes total. At the same time, grill the bell pepper quarters and zucchini rounds 3–4 minutes per side until tender and slightly charred. Grill cherry tomatoes briefly if desired.
To serve, divide the rice pilaf among bowls, top with chicken souvlaki, arrange grilled vegetables and tomatoes on the side, sprinkle with crumbled feta and mixed herbs, and serve with tzatziki.