Toast mustard seeds in a dry skillet over medium-high heat until they pop (about 1 minute).

Transfer toasted mustard seeds to a plate.

Heat 1 tablespoon of vegetable oil in the same skillet.

Add curry powder and cook until fragrant (about 1 minute).

Pour the curry-infused oil into a medium bowl and let it cool.

Cook snow peas in boiling salted water until bright green (about 1 minute).

Drain and cool the snow peas under cold water, then pat dry.

Slice snow peas lengthwise into thin strips.

Gently toss sliced avocado with lemon juice in a separate bowl to prevent browning.

Whisk together rice vinegar, dill, sugar, and the remaining 3 tablespoons of vegetable oil into the cooled curry oil.

Season the dressing with salt to taste.

Add the snow peas, red pepper, red onion, and flaked tuna to the dressing.

Toss gently to coat the ingredients.

Carefully fold in the avocado.

Serve immediately.