Season steaks with salt and pepper. Heat a large skillet over medium-high. Add steak and cook until medium rare, 3 to 5 minutes per side. Transfer to a plate to rest.
Return skillet and reduce heat to medium. Add butter to pan and cook until melted. Add Brussels sprouts; season with salt and pepper. Cook, stirring occasionally until crisp-tender, 3 to 5 minutes. Remove from heat and stir in almonds and lemon juice.