Preheat oven to 450°. Mix mayo ingredients in a small bowl; chill. Cook bacon until crisp in a 12-in. frying pan, transfer to paper towels, and reserve fat in pan.
Cook sardines skin side down in fat (in 2 batches if needed) over medium-high heat until opaque, tipping pan often and spooning fat over fish. Drain fish on paper towels.
Spread rolls with parsley chive mayo. Layer arugula, tomatoes, bacon, and sardines in rolls and cut in half.
*Ask your fishmonger to clean and fillet sardines for you, or do it yourself (see "How to Clean and Fillet Sardines" at sunset.com/smartseafood).