Preheat the oven the 400. Cut the beets into 8 wedges per beet. Place them on a rimmed baking sheet, drizzle with the olive oil, season with salt and pepper and toss to coat. Spread them out in a layer and roast for 30 minutes, turning once. Set them aside to cool.
Using a dry skillet, toast the walnuts over medium heat until starting to brown. Set them aside to cool.
Peel the oranges, removing all the pith. Cut out each segment of the orange between the membranes, dropping them into a bowl. Squeeze what's left of the orange into another larger bowl to be used in the dressing.
Make the dressing by whisking the dressing ingredients in the bowl with the orange's juice. Slice the fennel very thinly into the bowl and toss so that it doesn't discolor.
Add the watercress and arugula to the bowl with the fennel and toss to combine. To serve place the lettuce fennel mixture on a platter. Top with the beets and blood oranges and then sprinkle the toasted walnuts on top.
Notes
Beets - purple is pretty, but you can use any color.
Blood Oranges - can use regular oranges or grapefruit.
Fennel Bulb - can omit if you don't like the flavor of fennel.