Heat oven to 350℉. Line a 9x13 baking dish with parchment paper.
In large bowl, add the flour, quick oats, brown sugar, melted butter, pecans, and salt. Stir together until combined and crumbly. Remove a slightly heaping 1 cup and set aside for later.
1½ cups all-purpose flour, 1½ cups quick cooking oats, 1 cup packed light brown sugar, 1 cup (2 sticks) butter, 1 cup finely chopped pecans, ¾ teaspoon salt
Press the remaining mixture firmly into baking pan to form an even crust.
In saucepan over medium heat, add the condensed milk, semi-sweet chocolate chips, and butter. Let it cook, while stirring occasionally, until it's smooth and melted.
1 can (14 oz) sweetened condensed milk, 1 cup semi-sweet chocolate chips, 2 tablespoons butter
Pour the melted chocolate mixture over the crust in pan. Sprinkle with the reserved crust mixture (set aside from earlier). Sprinkle the mini red and green m&m's over top.Press down lightly with clean hands (this helps the m&m's and crust mixture stay in place). 1 cup red and green Christmas mini m&m's
Bake for 25 minutes. The edges should be lightly golden brown and pulled away from the edges of the pan.
Remove the pan from the oven and let the bars cool inside the pan, at room temperature, for 2 hours before cutting into squares.