1. Thaw empanada discs. Set cream cheese out to soften. Preheat oven to 375°F. Line 2 baking sheets with parchment paper. Zest lemon (1 teaspoon), then juice (2 tablespoons).
2. Place guava paste in microwave-safe bowl. Microwave on HIGH 1–2 minutes, stirring every 30 seconds, until smooth. Place cream cheese, lemon zest, and lemon juice in large bowl. Beat with electric mixer until blended and smooth.
3. Arrange empanada discs on work surface. Spoon cream cheese mixture onto discs (about 2 teaspoons each), then spoon guava paste over cream cheese mixture (about 2 teaspoons each).
4. Whisk egg and water until blended; brush edges of discs with mixture. Fold discs in half over filling, pinching edges to seal.
5. Arrange empanadas on prepared baking sheets; brush tops with remaining egg mixture. Bake 16–18 minutes until golden. Let stand on baking sheets 10 minutes before transferring to wire racks. Dust with powdered sugar before serving. Serve warm.

Chef's Tip: Want to fry? Heat vegetable oil in Dutch oven to 325°F. Prepare empanadas though step 4 (do not brush outsides with egg). Fry (in batches) 2–3 minutes on each side until golden. Remove from oil carefully; cool on wire rack–lined baking sheet 10 minutes before dusting with powdered sugar.