The researchers divided the participants into 4 groups and provided all of the food. The diets differed only by fatty acid composition. The participants ate either a:

Lunch rich in monounsaturated fat (17 grams; dinner contained only 10 grams)
Lunch rich in polyunsaturated fat (15 grams; dinner contained only 9 grams)
Dinner rich in monounsaturated fat (15 grams; lunch contained only 11 grams)
Dinner rich in polyunsaturated fat (15 grams; lunch contained only 9 grams)

The researchers measured glycemic control metrics with an oral glucose tolerance test.

The type of fat did not affect the results, but the timing of the fat intake did. Postprandial insulin levels were lower (better) and insulin sensitivity was higher (better) in the groups that consumed more unsaturated fat at lunch. There were no differences for blood glucose levels.

Does the timing of unsaturated fat intake influence insulin sensitivity? Original paper