Preheat the grill to medium-high heat.

Cut each fingerling potato crosswise into 2 to 4 pieces, depending on size.

In a shallow pan, combine 1 tablespoon of vegetable oil, 1/4 teaspoon of ground cumin, 1/4 teaspoon of salt, and 1/8 teaspoon of ground black pepper.

Add the potatoes to the pan and toss to coat them evenly with the oil and spices.

Add the green onions and jalapeno chile to the pan and toss to coat them.

Place the potatoes and jalapeno chile on the preheated gas grill or charcoal grill, positioning them 4 to 6 inches from the heat source. Cover the grill.

Grill for 8 to 12 minutes, or until the potatoes are evenly browned and tender, turning every 4 to 5 minutes to ensure even cooking.

Add the green onions to the grill. Grill, uncovered, for 4 minutes, or until they are browned and tender, turning once to cook both sides.

Transfer the grilled vegetables to the same shallow pan.

Allow the vegetables to cool slightly until they are cool enough to handle comfortably.

Halve the potato pieces if desired, adjusting the size according to your preference.

Peel the jalapeno chile, then carefully remove the veins and seeds for a milder flavor (or leave them in for extra heat).

Chop the peeled and deveined jalapeno.

Slice the grilled green onions.

In a large bowl, combine the grilled potatoes, chopped jalapeno, and sliced green onions.

Add the white wine vinegar, the remaining 1 tablespoon of vegetable oil, 1/4 teaspoon of cumin, 1/4 teaspoon of salt, and 1/8 teaspoon of ground pepper to the bowl.

Toss all ingredients together until they are well mixed and evenly coated with the dressing.

Allow the potato mixture to cool to room temperature.

Add the halved grape tomatoes to the cooled potato mixture and toss gently to combine.

In a small bowl, stir together the sour cream, prepared mustard, and chopped cilantro until smooth.

Pour the sour cream mixture over the potato mixture and stir gently until everything is thoroughly combined.

Serve the Grilled Southwest Potato Salad at room temperature or chilled.