Preheat oven to 400 degrees
Prepare the Ingredients
Trim ends off green beans. Cut into 1" pieces. Core pear and cut into ½" slices. Peel and halve shallot. Cut into ¼" slices. Mince garlic. Stem and mince thyme. Pat pork tenderloin dry, and season all over with ¼ tsp. salt and a pinch of pepper.
Start the Green Beans and Pear
Heat 2 tsp. olive oil in a large non-stick pan over medium-high heat. Add green beans, pear, shallot, ¼ tsp. salt, and ¼ tsp. pepper to hot pan. Stir occasionally until lightly charred, 5-7 minutes. If using chicken breasts, stir occasionally until lightly charred, 7-10 minutes. Transfer vegetables to prepared baking sheet and spread into a single layer (some overlap is ok). Reserve pan; no need to wipe clean.
Sear the Pork
Return pan used to start green beans and pear to medium-high heat. Add 1 tsp. olive oil and pork tenderloin to hot pan. Cook until browned on two sides, 3-4 minutes per side. If using chicken, cook until browned, 2-3 minutes per side.
Roast the Pork, Green Beans, and Pear
Place pork tenderloin on top of green beans and pear. Roast in hot oven until pork reaches a minimum internal temperature of 145 degrees, 16-18 minutes. If using chicken breasts, follow same instructions and roast until chicken reaches a minimum internal temperature of 165 degrees, 10-12 minutes. Rest pork at least 5 minutes, then slice if desired. Reserve pan; no need to wipe clean. While pork rests, make sauce.
Make the Sauce
Return pan used to sear pork tenderloin to medium heat. Add 1 tsp. olive oil, garlic, and thyme to hot pan. Cook until fragrant, 30-60 seconds. Stir in ¼ cup water and chicken base. Bring to a simmer and cook until slightly thickened, 1-2 minutes. Remove from burner and swirl in butter. Season with ¼ tsp. salt and a pinch of pepper.