Heat oil in a large Dutch oven or high-sided skillet over medium-high. Add sausage and press down on it with a heatproof rubber spatula to flatten slightly. Cook, undisturbed, until browned underneath, about 4 minutes. Turn sausage over and cook, undisturbed, until browned on the other side, about 3 minutes. Break up sausage into bite-size pieces with spatula.

Add sliced garlic, oregano, and red pepper flakes (if using) and cook, stirring, until garlic is beginning to get golden around the edges, about 1 minute.

Carefully add tomatoes (beware of splatter!), then 2½ tsp. salt and 1 cup water. Bring sauce to a simmer and cook, stirring occasionally, until slightly reduced, 10–12 minutes.

Mix in spinach and cook until wilted, about 2 minutes. Add beans and cook until warmed through, about 3 minutes. Taste ragù and season with more salt if needed.

Prepare the garlic toasts

Meanwhile, heat broiler. Heat olive oil in a small saucepan over medium heat. Mix in grated garlic and remaining ½ tsp. salt and cook until fragrant and sizzling but garlic is not yet browned, about 30 seconds; remove from heat.

Arrange bread, cut side down, on a foil-lined baking sheet and broil until golden brown, about 1 minute. Remove from broiler and turn bread over. Brush untoasted sides of bread with garlic oil and broil until evenly golden brown on top, about 1 minute (keep watch; it will go fast).

To serve

Divide toast among plates. Ladle a generous amount of ragù over and top with parsley.

Do Ahead: Ragù can be made 3 days ahead. Let cool; cover and chill. Reheat over medium-low.