1) Preheat the oven to 350°F. Lightly grease (or line with parchment) a large cookie sheet or a half-sheet (18" x 13") pan.
2) In a medium-sized bowl, beat together the butter, sugar, baking powder, cinnamon, salt, and vanilla till smooth.
3) Add the eggs and beat till the mixture is well combined. It may look a big coagulated. That's OK.
4) Add the flour and oats, mixing to combine.
5) Stir in the chips and nuts.
6) Divide the dough into four equal pieces, placing them on the prepared baking sheet.
7) Shape each piece into a rough log about 10" to 11" long, placing the logs crosswise on the sheet, and spacing them about 2" apart. Using your wet fingers and/or a wet spatula, flatten and smooth the logs till they're about 3/4" thick, and about 1 1/4" wide.
8) Spritz the top of each log with water, and sprinkle heavily with cinnamon-sugar.
9) Bake the logs for 23 to 25 minutes, until they're beginning to brown around the bottom edges. Remove them from the oven, and allow them to cool right on the pan for about 10 minutes. Spritz with water, sprinkle with more cinnamon sugar, and let them cool for another 15 to 20 minutes. While the logs are cooling, reduce the oven temperature to 325°F.
10) Cut the logs crosswise into 1/2" to 3/4" slices, using a sharp chef's knife.
11) Place the biscotti back on the baking sheet, spacing them close together without touching.
12) Bake the biscotti for 25 minutes, until their cut edges are a light golden brown. Remove them from the oven, and cool on the pan.