In a mixing bowl combine the chicken cubes with 1 tbsp butter, minced garlic, 1/2 jalapeño (seeded), 1/2 tsp ground cumin, 1/2 tsp cayenne, 1/2 tsp garam masala, 1/2 tsp minced ginger, 1/4 tsp salt, 1/4 tsp black pepper, 1 tbsp lemon juice, 2 tbsp plain yogurt and a pinch of cinnamon; mix well, cover and refrigerate for at least 1 hour.
Line a baking pan with aluminum foil and arrange the marinated chicken in a single layer, discarding excess marinade; grill in a preheated oven at 450°F (232°C) for 6–7 minutes, flipping once, until cooked through.
While the chicken cooks, combine the sauce ingredients in a bowl: 4 oz tomato sauce, 2 tbsp plain yogurt (for sauce), 2 tbsp heavy cream, 1/2 tsp cumin, 1/2 tsp paprika and 1/2 tsp garam masala; set aside.
In a small saucepan melt 1 tbsp butter over medium heat, sauté the minced garlic and jalapeño until aromatic, then add the spice mix and cook 1–2 minutes until fragrant; remove and discard the jalapeño.
Add the prepared tikka masala sauce to the saucepan, season with salt to taste, and simmer until slightly thickened, about 2 minutes; turn off the heat and stir in the cooked chicken to coat it in the sauce.
Preheat the oven to 450°F (232°C). Place the pizza crust on a pizza pan and lightly brush with olive oil.
Spread the chicken tikka masala mixture over the crust, sprinkle with 1/2 cup mozzarella, arrange the sauced chicken on top, add the thinly sliced 1/4 onion and chopped cilantro, then sprinkle the remaining mozzarella over everything.
Reduce oven temperature to 425°F (218°C) and bake the pizza for 8–10 minutes, until the cheese is melted and the crust is golden; remove and garnish with remaining cilantro before serving.