Heat oil in a large stainless steel pot over medium heat. Be patient! It will take a few minutes. Once you see a few wisps of smoke, it's ready. If there's a lot of smoke, it's too hot; remove from heat and cool.
Add the kernels and cover tightly with lid. Shake the pan to evenly coat the kernels with oil. Wait for the popcorn to start popping.
When the popcorn starts popping, shake the pot and slide back and forth over the burner. All the unpopped kernels will sink to the bottom while the popped kernels rise to the top. Shaking the pot will ensure even popping!
The popcorn is done when popping slows down to several seconds between pops. Immediately remove from heat and divide between two 13x18" sheet pans. Sprinkle salt (1/4 tsp per sheet pan) over warm popcorn and toss quickly with hands. Set aside.
In a microwave proof container, add chocolate chips and 1 tsp oil. Mix gently with a spoon. Heat in microwave for 15-30 second bursts, opening the door of the microwave each time to prevent condensation build up and stirring after each round. When the chips are halfway melted but still somewhat firm, they are done. Stir gently and the residual heat should gently melt the rest of the chocolate chips.
Using the same spoon, drizzle the melted chocolate over the popcorn in a diagonal motion. Evenly and quickly, cover both sheet pans with chocolate drizzles. A few clumps of chocolate are ok but try to keep the chocolate evenly distributed for best flavor and texture.
Sprinkle mini M&Ms on top. Make sure the M&Ms are touching the chocolate so it can stick. Then sprinkle flaky sea salt all over.
Transfer sheet pans to the refrigerator for at least 30 minutes. The chocolate should harden.
Remove from the fridge and transfer to a large bowl, breaking up the big pieces into smaller sized chocolate covered popcorn chunks. Alternately, you can serve on the sheet pans. But I recommend breaking up the large chunks of chocolate covered popcorn first. Enjoy!