Heat oven to 425°F. Toss sweet potato and poblano with oil, cumin and 1/4 teaspoon salt on a sheet pan; roast for 25 to 30 minutes, turning once, until tender and browned.
Reduce oven to 350°F. Butter a 9-by-13-inch baking dish, whisk eggs with milk and remaining salt, pour into the dish and bake for 14 to 18 minutes until just set and 160°F in the center. Cut into short strips.
Spread vegetables and egg strips in shallow containers, refrigerate within 2 hours and chill completely before assembly. Refrigerate the beans and cheese too.
Divide vegetables, egg strips, beans and cheese evenly across the tortillas. Fold in the sides and roll tightly; wrap each burrito separately, put in a freezer bag and freeze for up to 2 months for best quality.
To reheat one from frozen, remove all wrapping and loosely wrap in a damp paper towel. Microwave on a microwave-safe plate at 50 percent power for 3 minutes, turn, then heat at full power in 1-minute intervals, usually 2 to 4 more minutes, until the center reaches 165°F.
Rest for 1 minute, then toast in a dry skillet over medium heat for 1 to 2 minutes per side if you want a firmer tortilla. Check the middle again if any part still feels cool.