Preheat the oven to 350 degrees F. In a large saute pan, over medium heat, add the oil. When the oil is hot, add the onions. Season with salt and pepper. Saute until caramelized, about 15 minutes, stirring occasionally. Remove from the heat and cool completely.
Using an electric mixer with a dough hook, whisk the yeast, sugar, garlic, 2 tablespoons of the olive oil, warm water, and caramelized onions together for 2 minutes to dissolve the yeast. Add the salt and flour. With the mixer on low, mix until the dough starts to come together. Increase the speed to medium-high and mix until the dough comes away from the sides of the bowl and crawls up the dough hook. Grease a mixing bowl with 1 teaspoon of the oil. Place the dough in the greased bowl and turn once. Cover the bowl with plastic wrap and place in a warm, draft free place until the dough doubles in size about 1 1/2 hours. Grease a half baking sheet pan (17 by 12) with 2 teaspoons of the oil. Turn the dough out onto a baking sheet. Punch the dough down and press the dough out to form the pan. Brush the dough with remaining 1/4 cup of the olive oil. Sprinkle the dough with kosher salt and coarse black pepper. Lightly cover the pan with plastic wrap and let the dough rest for 1 hour. Bake the dough for 30 to 35 minutes or until the dough is golden brown. Slice the bread into individual pieces or into sandwich slices.