1. In a medium, non-stick skillet cook beef until no longer pink – approximately 5-7 minutes.
2. Stir in ketchup and mustard and continue to cook until warmed through.
3. Remove from heat and set aside to cool.
4. In a small bowl, stir together Greek yogurt and salsa; cover and refrigerate until ready to use.
5. Layer remaining ingredients equally into two mason jars starting with the Greek yogurt/salsa mixture, beef mixture, tomatoes, pickles, onion, cheese, and lettuce.
6. Cover jars with lids and refrigerate until ready to use.