In a large nonstick skillet, cook the bacon over medium, turning once, until crispy, 6 to 7 minutes. Transfer to a paper towel-lined plate. Let cool; chop.
Discard the fat from the skillet. Add 1 tbsp. oil; heat over medium. Add the Brussels sprouts; season with salt and pepper. Cook, stirring occasionally, until crisp-tender, 7 to 8 minutes; transfer to a bowl.
In the same skillet, heat the remaining 1 tbsp. oil. Add the onion, garlic and thyme; cook, stirring often, until starting to soften, 1 to 2 minutes. Add the barley; cook, stirring constantly, until lightly toasted, about 1 minute. Add the stock; season. Bring to a boil, then reduce the heat to medium-low. Cover the risotto and simmer until the barley is tender, 10 to 12 minutes.
Season the shrimp. Add to the risotto and increase the heat to medium-high. Cook, uncovered, until almost all the liquid evaporates, 2 to 3 minutes. Stir in the bacon and Brussels sprouts. Cook until the shrimp are opaque, 1 to 2 minutes. Remove the risotto from the heat and stir in the Parmesan; season.