Bring a large pot of salted water to a boil. Blanch the kale leaves in the boiling water for 15 seconds, and them transfer them to a sieve. (Leave the boiling water on the stove to use for the pasta.) Using a spatula, press the kale leaves firmly into the sieve to release as much water as possible. Transfer the kale leaves to a blender.
Add the toasted pumpkin seeds, Parmesan, garlic, salt and pepper to the blender and pulse briefly to combine the ingredients. With the blender running, stream in the olive oil and continue blending, scraping down the sides of the blender as needed, until the mixture is a smooth puree. Set the pesto aside.
Heat a large saute pan over medium heat. Rinse and thoroughly dry the chicken breasts. Sprinkle them liberally with salt and pepper.
Add the butter to the heated pan. Place the chicken breasts in the pan and allow them to cook until they naturally release from the pan. Flip the chicken breasts once and continue cooking until they reach 165 degrees F on an instant-read thermometer and are no longer pink.
While the chicken cooks, add the linguine to the pot of boiling salted water and cook until al dente, 9 to 11 minutes.
Drain the pasta and transfer it to a large bowl. Add the pesto to the bowl, tossing to combine. Slice the seared chicken breast and serve it alongside the pasta.
You could also sear the chicken breasts in an ovenproof skillet then bake in a 350 degree F oven until they reach 165 degrees F on an instant-read thermometer.