In a small bowl, whisk the lemon juice, vinegar, Dijon, and sea salt to combine. When the mixture is well combined, slowly drizzle in the olive oil, whisking vigorously until vinaigrette is nicely emulsified.
For the salad:
Preheat oven to 375° F. In a small bowl, whisk together the olive oil and Champagne vinegar.
Halve pears and carefully cut out the core. Set pears with sliced side facing up on a rimmed baking sheet. Drizzle olive oil mixture over pears and sprinkle each with sea salt and pepper.
Slide the baking sheet into the oven. Roast for 8 minutes, then use tongs to flip the pears, and return them to the oven for 6 to 8 more minutes, or until the edges are golden and the pears are easily pierced with a fork. Set aside to cool.
In a large bowl, toss the greens with half of the vinaigrette. Crumble in chèvre and toss gently. Divide greens between four plates, add 2 pear halves to each, and drizzle with the remaining dressing. Finish salads with a pinch of sea salt and a liberal sprinkle of black pepper, and garnish with a lemon wedge.