1. Preheat oven to 425°. Coat onion with 1 tbsp. oil. Roast in a pie pan, cut side down, until soft when pressed, 40 to 45 minutes. Discard dark outer layer. Slice onion crosswise.
2. Toast bread and almonds in a large frying pan over medium-low to low heat, stirring occasionally, until bread is crisp but not brown, 7 to 8 minutes. Add 3 tbsp. oil, the onion, peppers, garlic, paprika, and chile flakes. Cook, stirring occasionally, until garlic is softened, 8 to 12 minutes.
3. Purée mixture in a food processor with remaining 5 tbsp. oil, the vinegar, lemon juice, and salt.
Make ahead: Up to 1 week, chilled; serve at room temperature.