In short, the key to achieving both is to adopt a diet that's low in simple/refined carbohydrates (cakes, pastries and white varieties of bread, rice and potatoes), while also remaining low in the consumption of salt and saturated animal fats.
To reduce the secretion of insulin, carbohydrate should be obtained from complex sources, such as beans, pulses and wholegrains, thus ensuring that glucose is released into the bloodstream at a more sustained level after digestion.
As for high blood pressure, the recommendation of a diet that's low in consumption of salt/sodium and saturated animal fat is best advised, as means of improving blood flow both from and back to the heart.
Granted, salt is important for helping to maintain the correct balance of electrolytes, but the body requires far less than it invariably receives on daily basis. As such, reducing consumption of salt will also assist.
In addition to reducing consumption of simple sugars, salt and saturated animal fat, on the assumption that it's permitted, the introduction of regular exercise alongside a calorie controlled diet will also assist in improving blood pressure. Equally, the measured consumption of healthy fats (oils, seeds, nuts and fish), will serve to improve levels of HDL cholesterol (healthy), helping to reduce levels of LDL cholesterol (un-healthy) and corresponding levels of high blood pressure in the process.