How to Make It
Preheat oven to 350°F. In a large pan, mix tomatoes, oil, garlic, oregano, crushed red pepper, if desired, and 1/2 tsp. each salt and pepper. Bring to a boil over high heat. Reduce heat to low and simmer, stirring occasionally, until sauce has thickened slightly, about 20 minutes.
Place bagel halves on a parchment-lined baking sheet. Spread 2 Tbsp. sauce onto each bagel half. (Cover and refrigerate or freeze any remaining sauce for another use.) Top each with 1 rounded Tbsp. shredded cheese.
Slice 1 olive in half lengthwise. Place 1 olive half, cut side down, in center of 1 bagel half to make a spider body. Slice remaining olive half into 8 thin crescents to make 8 spider legs. Arrange 4 legs on each side of body to complete spider. Repeat with remaining olives and bagel halves until all bagel pizzas are decorated.
Bake pizzas until toasted and cheese has melted, 10 to 12 minutes. Serve.