Place tortillas in the bowl of a food processor; process to form fine crumbs.
Heat a 6-quart pressure cooker over medium-high heat. Add 1 teaspoon oil to pan; swirl to coat. Sprinkle beef with 1/2 teaspoon salt. Add one-third of beef to pan; sauté 3 minutes or until browned on all sides. Remove beef from pan. Repeat procedure twice more with 1 teaspoon oil and one-third of beef.
Add remaining oil to pan; swirl to coat. Add onion and garlic; sauté 3 minutes. Add tortilla crumbs, chili powder, and next 8 ingredients; stir well. Stir in beef.
Close lid securely; bring to high pressure over high heat (about 4 minutes). Adjust heat to medium-high or level needed to maintain high pressure; cook 25 minutes. Remove from heat; let stand 20 minutes. Place cooker under cold running water to release pressure. Remove lid; stir in chocolate and remaining salt, stirring until chocolate melts. Top with green onions and radish, if desired.
Dutch Oven: Using a large Dutch oven, follow instructions through step Bring mixture to a boil; cover and bake at 300° for 2 1/2 hours, stirring two or three times to prevent sticking. Stir in chocolate and remaining salt to finish.
Slow Cooker: Using a large skillet, follow instructions through step Transfer to a 6- or 7-quart slow cooker. Cover and cook on LOW 8 hours. Stir in chocolate and remaining salt to finish.
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