Peel, halve, and slice onion crosswise into thin half-moons. Place in a small bowl.

Preheat a skillet over medium heat.

While the skillet heats up, peel and mince garlic. Add to the bowl with the onion.

Once the skillet is hot, add butter and swirl to coat the bottom. Add onion and garlic; cook, stirring occasionally, until golden and caramelized, 15-18 minutes. (Reserve bowl for later use.)

Meanwhile, wash, dry, and slide thyme leaves off the stems; discard the stems. Place leaves in another skillet.

Add orzo, broth, Worcestershire, salt, and pepper to the skillet with the thyme. Stir to combine and bring to a simmer over high heat. Once simmering, reduce heat to medium-low and cook, stirring occasionally, until liquid is mostly absorbed, about 10 minutes. Remove from heat.

While the orzo is cooking, finely grate mozzarella. Place in the reserved bowl and set aside.

Wash and dry spinach (skip this step if it came pre-washed.)

When the onions are caramelized, carefully transfer them to the skillet with the orzo. Stir to combine. (Reserve skillet for later use.)

Add spinach to the skillet with the orzo in handfuls, waiting for it to wilt slightly before adding the next handful. Return to medium-high heat and continue to cook until spinach is completely wilted, 2-3 minutes more.

Once the spinach is wilted, remove from heat, sprinkle with grated cheese, and cover with a lid. Set aside until cheese is melted, 3-4 minutes.

Meanwhile, return skillet used for the onions to medium-high heat. Add more butter and swirl to coat the bottom. Add bread slices and pan-fry until toasted on one side, about 1 minute.

Remove bread to a plate and add more butter to the skillet. Return bread to the skillet, toasted-side up, and continue to pan-fry until toasted on the other side, 1 minute more. Return to the plate.

Divide orzo between plates or bowls. Serve with toasted sourdough on the side and enjoy!