Bring a large pot of salted water to a boil and cook the gluten-free pasta according to package instructions, about 2 minutes less than directed for al dente; drain and set aside.
While the pasta cooks, heat the avocado oil in a large skillet over medium-high heat.
Add the finely chopped onion and sauté, stirring occasionally, until softened, about 5 minutes.
Stir in the minced garlic and chopped chicken; let the chicken brown without stirring for a couple minutes, then continue cooking and stirring until the chicken is browned but not fully cooked, about 2–3 more minutes.
Pour in the full-fat coconut milk, add lemon zest, lemon juice, and sea salt, and stir to combine.
Bring the sauce to a gentle boil, then reduce to a simmer and cook until the chicken is cooked through, about 5 minutes.
Toss the drained pasta into the skillet with the sauce until well coated and heated through.
Stir in chopped basil if using and taste; adjust with more sea salt or lemon juice as desired before serving.
