In a large pot, heat oil. Saute onion in oil until it's translucent and tender, about 5 minutes.
Add the broth, tomatillos, bell pepper, jalapeño and salt. Bring to a boil then cook on high for 10 minutes, or until vegetable soften, tomatillos have turned olive green and the sauce starts to thicken.
Remove from heat and add avocado, cilantro and garlic. Using an immersion blender or blender, blend the sauce mixture to desired texture (TIP: It's ideal to leave some texture, similar to a chunky marinara sauce).
While the sauce is cooking, in a separate pot, cook black bean pasta according to package directions.
Serve sauce over noodles. If desired, top with crumbled queso fresco.