In a large bowl combine the chicken chunks, 1/4 cup olive oil, smoked paprika, ground cumin, 1/2 teaspoon turmeric, grated garlic (6 cloves), lemon juice and zest, crushed red pepper flakes, and a generous pinch of kosher salt and some black pepper; toss to coat and marinate at least 15 minutes or up to overnight in the refrigerator.
While the chicken marinates, preheat the oven to 425°F (220°C) and arrange a rack in the center.
Toss the matchstick potatoes with the 3 tablespoons olive oil, 1 teaspoon turmeric, cayenne (1/4–1/2 teaspoon), the smashed garlic cloves, and a large pinch of kosher salt on a large baking sheet; spread in a single layer without overcrowding (use two sheets if needed).
Bake the fries 15–20 minutes, flip or shake the pan, then bake another 15 minutes; add the 2 tablespoons salted butter, toss to coat, and return to the oven 5 minutes more until tender and crispy.
Make the garlic sauce by combining the yogurt (or avocado mayo), 2 cloves grated garlic, 2–3 tablespoons lemon juice, and a pinch of salt; taste and adjust lemon or salt as desired.
Heat your grill, grill pan, or skillet to medium-high. Thread the marinated chicken onto skewers and grill, turning occasionally, until lightly charred and cooked through, about 10–12 minutes total.
Grill the halved shallots alongside the chicken for 2–3 minutes per side until tender and slightly charred. Alternatively, roast the chicken at 400°F (200°C) for 20–30 minutes if not grilling.
In a small bowl combine the remaining 3 tablespoons olive oil, the chopped mixed herbs, and a pinch of salt to make the herb oil; toss with the grilled shallots.
Serve the chicken topped with garlic sauce and drizzled with herb oil and the shallots, alongside the golden butter fries and warmed naan if desired.