Bring a large pot of lightly salted water to a boil. Add rotini and liquid smoke; cook at a boil until rotini is tender yet firm to the bite, about 8 minutes.

While pasta is cooking, heat olive oil in a large skillet over medium-high heat. Add diced bratwurst, 2 tablespoons green onions, and garlic; cook until bratwurst is brown and crispy, 4 to 5 minutes. Remove from heat and allow to cool.

Combine yellow and orange bell peppers, celery, parsley, mustard, mayonnaise, water, vinegar, sugar, and black pepper in a large bowl; stir to combine.

Drain pasta and add to vegetable mixture. Add bratwurst, onions, and garlic and stir gently until all ingredients are combined. Serve warm or cold.