Mix the chili powder, paprika, salt, and black pepper in a small bowl. Pat the chicken completely dry with paper towels, then coat evenly on both sides with the spice rub. Let it sit at room temperature for 15 minutes. Drying the surface is essential for a proper sear.

Heat vegetable oil in a heavy skillet or cast-iron pan over medium-high heat until shimmering. Add the chicken and sear for 5 to 7 minutes per side without moving it. The chicken should be deep golden brown and reach an internal temperature of 165 degrees F. Transfer to a cutting board and rest for 5 minutes before slicing.

While the chicken rests, make the creamy garlic sauce. Melt butter in a small saucepan over medium heat. Add minced garlic and cook for 60 seconds until fragrant. Pour in the heavy cream, stir, and simmer for 2 to 3 minutes until slightly thickened. Remove from heat and set aside.

In a separate medium pot, heat sesame oil over medium heat. Add minced garlic and saute for 60 seconds. Pour in the chicken broth and soy sauce, then stir in the heavy cream. Bring to a gentle simmer and cook for 5 to 7 minutes. Taste and adjust seasoning.

Cook the ramen noodles in boiling water according to package directions, pulling them about 30 seconds before the package says they're done since they continue to soften in the hot broth. Drain well and set aside.

Divide the noodles between bowls. Ladle the hot broth over the noodles. Top with sliced chicken and drizzle the creamy garlic sauce over everything. Garnish with chopped green onion and chili oil if using. Serve immediately.