Cooking bacon in the oven on a sheet tray is so hands-off, so splatter-free, and so easy, it just might convince you to eat a lot more bacon in the future.
Preheat oven to 350°. Arrange 8 bacon slices side by side on a small rimmed baking sheet, overlapping slightly if necessary.
Bake bacon, removing sheet from oven and turning slices with tongs halfway through, until slices are deep reddish brown with crispy edges, 25–35 minutes. Increase oven temperature to 425°.
While bacon is cooking, cut crusts off bread; discard. Tear bread into 1" pieces. Don’t worry if the pieces end up in different shapes and sizes. Irregular is good! You should have about 2 lightly packed cups.
Transfer bacon to a paper towel–lined plate and blot with more paper towels to absorb excess fat. The bacon will crisp as it cools. Reserve baking sheet with bacon fat.
Scatter bread on reserved baking sheet and toss with tongs until bread is evenly coated in fat.
Bake bread, tossing once halfway through, until pieces are golden all over and crisp, 10–15 minutes. Let cool.
Meanwhile, whisk ⅓ cup mayonnaise and 2 Tbsp. lemon juice in a medium bowl. Season with salt and lots of pepper, then slowly stream in ⅓ cup oil, whisking until dressing is thick and emulsified. Whisk in a pinch of sugar; set aside.
Thinly slice enough chives to measure 2 Tbsp. and whisk into bowl with dressing.
Slice remaining chives into 1" pieces; set aside.
Halve 2 romaine hearts lengthwise, trim off root ends, then cut each half in half again crosswise. Arrange lettuce pieces on a large platter or divide among individual plates. Season with salt and pepper and drizzle about a third of the dressing over top.
Arrange tomatoes, avocado, and croutons over and around lettuce pieces.
Break up cooled bacon with your hands into rough 1" pieces and scatter over salad. Drizzle with remaining dressing.
Sprinkle with reserved chives and serve.