In a large skillet, heat olive oil over medium-high heat. Salt and pepper beef cubes. Once pan is hot, toss butter into pan, then immediately add steak. Cook until golden brown on one side, then turn in pan, cooking until golden brown on other sides. Add garlic and balsamic to pan. Cook, stirring often, until vinegar begins to thicken. Remove from heat and transfer into 1-cup section of meal prep container.
In a large pan over medium heat, cook frozen cauliflower until warm. Add garlic puree and stir in baby spinach. Transfer to 2-cup section of meal prep container.