Heat 3 Tbsp. vegetable oil in a medium Dutch oven or other heavy pot over medium. Add 1 tsp. cumin seeds; cook, stirring often, until fragrant and seeds begin to pop, about 2 minutes.

Add ½ medium red onion, finely chopped, 1 serrano chile, finely chopped, one 1" piece ginger, peeled, finely chopped, and 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt. Cook, stirring occasionally, until onion is softened, about 3 minutes.

Add 1 lb. russet potatoes (about 2 large), peeled, cut into ½" cubes, 1 Tbsp. curry powder, and 1½ cups water and bring to a boil. Cover and cook, stirring often and adjusting heat as needed to maintain a simmer, until potatoes are tender and water is mostly absorbed, 15–20 minutes.

Remove from heat and stir in ½ bunch cilantro, leaves and tender stems only, coarsely chopped, 1 cup frozen peas, preferably baby, and 1 Tbsp. fresh lime juice, smashing potatoes into a chunky purée. Taste and season with more salt if needed.

Lay out four 8"–10" whole wheat tortillas on a work surface. Scatter 8 oz. pepper jack cheese or sharp white cheddar, coarsely grated (about 2 cups), over tortillas, covering evenly. Divide potato filling among tortillas, spooning over one side. Fold tortillas up and over filling to make half-moons; pat to flatten slightly.

Heat 1 tsp. vegetable oil in a large nonstick skillet over medium. Place 2 samosa-dillas in pan and cook, turning halfway through, until tortillas are golden and cheese is melted, about 5 minutes. Transfer to a cutting board. Repeat with remaining 1 tsp. vegetable oil and remaining 2 samosa-dillas. Cut samosa-dillas into wedges and transfer to plates.

Toss 2 mini seedless or Persian cucumbers, quartered lengthwise, sliced ¼" thick on a deep diagonal, 4 oz. cherry tomatoes (about 1 cup), halved, and ½ medium red onion, thinly sliced, in a medium bowl. Drizzle generously with lime juice and season with a large pinch of salt; toss to coat. Spoon some salad alongside each samosa-dilla.