Using a vegetable peeler, peel four 3-inch strips of lemon peel, making sure to avoid white pith; reserve lemon for later. Add lemon peels to a small skillet with oil and shallot.
Heat skillet over medium and cook, stirring occasionally, until shallot starts to brown and lemon peels start to curl and toast, about 3 minutes.
Add pecans and cook, stirring frequently, until pecans are browned, 3–4 minutes.
Off heat, stir in fennel seeds and let rest 2 minutes.
Strain oil through a fine mesh sieve set over a small liquid measuring cup.
Spread nut and spice mixture onto a plate and sprinkle with flaky sea salt.
Once cool enough to handle, mince lemon peels and add back to nut and spice mixture.
Juice reserved lemon and add 2 tablespoons lemon juice, Dijon and honey to measuring cup with infused oil; whisk to combine then season with kosher salt and pepper to taste.
Arrange arugula and pear slices on a large platter or serving bowl. Sprinkle blue cheese and toasted nut and spice mixture over salad. Drizzle vinaigrette over top and serve.