1 - 1.5 skiens of Koigu depending on how much ribbing you like (I used possibly 622 or 816.)
4 US 2 dpns
1 extra Us 2 dpn or two markers for the thumb
Cast on 46 sitches and join in the round as you knit knit 1, purl 1 ribbing. I used 7 rows of ribbing. Make sure your cast on is fairly loose, since this will be the part over your fingers.
[Insert Walker's Flame Chevron pattern here]
Knit the above lace pattern for 1 repeat. After row 24, find a place to add your thumb. Cast on a multiple of 7 stitches for the thumb using a provisional cast on. You could easily use another cast on, since the ribbing around the thumb will hide any twisted stitches. I used 14 stitches. Complete your row if need be. Your thumb can be placed anywhere so as to encourage the flash to be on one side of your hand. For rows 1 - 7, do make the make 1's for your thumb area.
Now, begin decreasing. On row 8, do not make the make 1's. After row 8, you will have 12 thumb stitches. Continue, either placing your decreases in a subtle place at the edge of the hand, or place your decreases following the path laid out by the previous ones. If you do this latter option, you must move your decreases on row 14 to better follow the shift in the pattern. After row 20, no stitches will remain of your thumb gusset. Complete the full repeat of your lace and try the mitt on. If it is long enough, make 7 rows of knit 1, purl 1 ribbing, and then preform a stretchy bindoff of your choice.
By reducing your number of repeats, you could easily do this in worsted weight yarn. To get the flash, you'll need any yarn that is prone to flashing and that flashes at your chosen gauge. I suspect Lorna Laces Shepherd Worsted would be amazing. On the cheaper end of things, Knitpicks has a discount sock yarn that flashes, and TLC / Red Heart / Caron all have variagated yarns which tend to flash.