To medium saucepan set over medium-high heat, add 5 cups water, 1 packet chicken bouillon, bay leaves, 1/2 tsp. Adobo. Bring to a boil, add chicken and bring back to a boil. Reduce heat to a simmer and cook, stirring occasionally, for 12 to 15 minutes or until chicken is tender and cooked through and an instant-read thermometer registers 165°F when inserted into thickest part of chicken.
Transfer chicken to cutting board (reserving poaching liquid) and let cool slightly. Using 2 forks, shred chicken.
In large skillet set over medium heat, add 2 tbsp. oil. Add onion and cook, stirring occasionally, for 2 to 3 minutes or until softened. Add potato and 1/4 cup poaching liquid and cook, stirring occasionally, for 8 to 10 minutes or until tender. Add peas and carrots and tomatoes and cook, stirring occasionally, for 3 to 5 minutes or until vegetables are tender-crisp. Add chicken and 2 tbsp. poaching liquid; stir to combine, then remove from heat.
Meanwhile, in medium bowl, stir together Masarepa, remaining packet chicken bouillon, packet Sazón, baking soda and remaining Adobo. Gradually stir in 2 1/2 cups poaching liquid and 1 tbsp. oil to form a soft dough. Knead for 5 minutes or until smooth.
Divide dough evenly into 12 small balls. Using wet hands, flatten balls into 5-inch discs and arrange in single layer on work surface or baking sheet. Divide chicken mixture evenly among discs and fold in half to enclose filling, pressing edges to seal.
In large, high-sided skillet set over medium heat, add remaining oil and heat to 350°F or until shimmering. In batches to avoid crowding, cook pasteles, flipping once, for 3 to 5 minutes or until golden and crispy. Transfer to paper towel–lined plate to drain. Serve with cabbage salad or Salvadorian-Style Pickled Vegetables.