Preheat oven to 350 degrees F. Line a 9x9 inch square baking pan with parchment paper so that there is some overhang on each side. Spray with nonstick spray.
Add flour, sugar, butter, salt, and black gel food coloring to a food processor. Pulse until combined.
Press the mixture into the prepared pan. Bake for 15 minutes, then let cool in pan for 15 minutes.
Add cream cheese to the bowl of a standing mixer fitted with a paddle attachment. Beat until fluffy. Add sweetened condensed milk and beat. Add lime juice, extract, and green gel food coloring. Beat until combined. Pour mixture over cooled crust.
Bake 30-35 minutes until set. Cool 30 minutes then cover with plastic wrap and refrigerate until chilled, 4 hours to overnight.
Add candy melts to a microwave-safe bowl and microwave in 30 second intervals, whisking in between, until melted. Transfer to a piping bag. Pipe out 9 snakes, about 2 inches tall, onto a parchment-lined baking sheet, using a toothpick to move chocolate around. Use a printed template if needed. Refrigerate until set, about 10 minutes.
Once snakes are dry, spray with metallic spray and let set.
Lift chilled bars from pan and cut into even squares, 3 across and 3 vertical, so you have 9 squares total.
Push mini M&M’s into the bars in offset rows to create a snake-like pattern.
Pipe some melted chocolate onto the back of the snakes and place in the center of the bars. Let dry before serving.