Combine oil, jalapeño, tomatillo, garlic, and lime juice in a blender; process until smooth, about 1 minute. Set dressing aside.
Working with 1 cucumber half at a time, place cucumber, cut side down, on a cutting board; using the bottom of a heavy skillet or pot, lightly crush cucumber. Repeat process with remaining cucumber halves.
Cut smashed cucumbers on a diagonal into ½-inch-thick slices. Transfer cucumber pieces to a large bowl, and toss with salt until well coated. Let stand for 15 minutes.
Transfer cucumber pieces to a colander, and rinse with cold water; drain well.
Toss together cucumbers and 6 tablespoons dressing in a large bowl; reserve remaining dressing for another use.
Top cucumber mixture with pepitas and queso fresco; garnish with cilantro leaves. Serve immediately.
