Step 1

Bring tomatillos, chiles, garlic, stock, and ½ cup cilantro to a simmer in a large saucepan over medium-high heat. Simmer 10 minutes. Let cool slightly, then transfer to a blender and blend until smooth. Return to pot and add beans; keep warm.

Step 2

Cook bacon in a large skillet over medium heat until brown and crisp, 8–10 minutes. Transfer to paper towels. Let cool, then crumble.

Step 3

Toast chiles in bacon fat over medium heat, tossing occasionally, until just beginning to darken. Transfer to plate with bacon. Wipe out skillet or wash to remove any dark spots.

Step 4

Heat 1 Tbsp. oil in skillet over medium. Cook spring onions, cut side down, until browned, about 5 minutes. Transfer to pot with beans. Add remaining 1 Tbsp. oil to skillet and increase heat to medium-high. Season steak with salt and pepper and cook until deep brown all over, about 5 minutes per side (it should be well browned on both sides but can be very rare in the center as it will cook more in the soup). Transfer to a cutting board and let rest at least 10 minutes before slicing against the grain about ¼" thick. Cut crosswise into 1" pieces. Add to soup; taste and season with salt and pepper if needed.

Step 5

Serve soup topped with bacon, chiles, cilantro, white onion, radishes, and avocado, with tortillas alongside.