In a medium bowl, combine chicken thighs, curry powder, 1/2 teaspoon salt, black pepper, and chili powder. Toss until chicken is evenly coated. Let rest for 10-15 minutes.
Heat 1 tablespoon oil in a large skillet or wok over medium-high heat until shimmering. Add chicken in a single layer and cook for 4-5 minutes, turning occasionally, until golden brown and cooked through. Transfer to a plate and set aside.
Add remaining 1 tablespoon oil to the same skillet. Add sliced onion and jalapeño, cooking for 3-4 minutes until onion softens and begins to caramelize.
Add minced garlic and grated ginger, stirring constantly for 30 seconds until fragrant. Be careful not to burn.
Pour in coconut milk and bring to a gentle simmer, scraping up any browned bits from the bottom of the pan with a wooden spoon.
Whisk together cornstarch and 2 tablespoons water until smooth. Slowly drizzle into the simmering sauce while stirring continuously. Cook for 3-4 minutes until sauce thickens enough to coat the back of a spoon.
Return chicken and any accumulated juices to the skillet. Stir gently to combine and heat through for 2-3 minutes.
Remove from heat. Immediately stir in torn basil leaves and lime juice. Taste and adjust seasoning with remaining salt if needed.
Serve immediately over cooked jasmine rice, garnished with extra basil leaves and lime wedges.
