Step 1

1 Make the sauce: In a small bowl, whisk together the soy sauce

Step 2

2 Dijon mustard and chili-onion crunch

Step 3

3 Make the tempura: In a medium bowl, whisk together the flour, cornstarch, baking powder, cumin, salt and pepper, then slowly add the seltzer while whisking until combined, being careful not to overmix

Step 4

4 In a 2- to 3-quart saucepan over medium-high heat, heat the oil until shimmering

Step 5

5 If vegetables were frozen, pat them dry to remove any residual moisture

Step 6

6 In a large bowl, mix the vegetables with the onion, then pour the batter over the vegetables and gently toss to coat

Step 7

7 Using a soup spoon or a small ice cream scoop, drop the coated vegetables into the hot oil

Step 8

8 Cook until crisp, 1 to 2 minutes on each side

Step 9

9 Using tongs or a slotted spoon, lift the fritters out of the oil and transfer to a wire rack set over a paper towel-lined large rimmed baking sheet to drain

Step 10

10 Repeat the frying with the remaining vegetables

Step 11

11 Serve with the sauce for dipping and lemon wedges to squeeze over the tempura