Adjust oven rack to middle position and preheat oven to 300°F.
Place cold mixture in bowl of food processor with onion, garlic, and bacon.
Process until smooth puree is formed, about 1 minute total, scraping down sides with rubber spatula as necessary.
Line rimmed baking sheet with aluminum foil.
With moist hands, form meat mixture into rectangle about 1 ½ inches high, 8-inches long, and 5-inches wide.
Bake until center of loaf reads 155°F on an instant read thermometer, about 30 minutes.
Allow loaf to rest at room temperature for fifteen minutes (or refrigerate for up to a week—see note)