Combine 1 tablespoon water and ½ teaspoon baking soda in small bowl.In a bowl, toss beef with baking soda mixture and ½ teaspoon salt until thoroughly combined. Set aside.
Heat oil in 12-inch nonstick skillet over medium heat until shimmering.
Add onion and remaining ⅛ teaspoon baking soda and stir to coat. Cook, stirring occasionally, until onion is softened, 3 to 4 minutes.
Add garlic and cook, stirring constantly, until fragrant, about 30 seconds.
Stir in sugar, paprika, pepper flakes, and remaining ⅛ teaspoon salt and cook, stirring constantly, until paprika is fragrant, about 1 minute.
Add tomato paste and cook, stirring constantly, until paste is rust-colored, 3 to 4 minutes.
Add beef and cook, breaking up meat with wooden spoon till no lumps remain, until beef is no longer pink, about 5 minutes.
Add ketchup, vinegar, and Worcestershire and stir to combine, scraping up any browned bits.
Combine cornstarch and remaining 1 tablespoon water in small bowl, then pour cornstarch mixture over beef and stir to incorporate.
Cook, stirring constantly, until sauce thickens and coats beef, about 1 minute. Spoon beef mixture onto buns and serve.
