Check this thread: Azure AKS Monitoring - custom dashboard resources

Also, here is a good query about cluster-wide cpu/memory utilization:

let endDateTime = now();
let startDateTime = ago(14d);
let trendBinSize = 1d;
let capacityCounterName = 'cpuCapacityNanoCores';
let usageCounterName = 'cpuUsageNanoCores';
KubeNodeInventory
| where TimeGenerated < endDateTime
| where TimeGenerated >= startDateTime
// cluster filter would go here if multiple clusters are reporting to the same Log Analytics workspace
| distinct ClusterName, Computer
| join hint.strategy=shuffle (
    Perf
    | where TimeGenerated < endDateTime
    | where TimeGenerated >= startDateTime
    | where ObjectName == 'K8SNode'
    | where CounterName == capacityCounterName
    | summarize LimitValue = max(CounterValue) by Computer, CounterName, bin(TimeGenerated, trendBinSize)
    | project Computer, CapacityStartTime = TimeGenerated, CapacityEndTime = TimeGenerated + trendBinSize, LimitValue
) on Computer
| join kind=inner hint.strategy=shuffle (
    Perf
    | where TimeGenerated < endDateTime + trendBinSize
    | where TimeGenerated >= startDateTime - trendBinSize
    | where ObjectName == 'K8SNode'
    | where CounterName == usageCounterName
    | project Computer, UsageValue = CounterValue, TimeGenerated
) on Computer
| where TimeGenerated >= CapacityStartTime and TimeGenerated < CapacityEndTime
| project ClusterName, Computer, TimeGenerated, UsagePercent = UsageValue * 100.0 / LimitValue
| summarize Avg = avg(UsagePercent), P95 = percentile(UsagePercent, 95), P90 = percentile(UsagePercent, 90) by bin(TimeGenerated, trendBinSize) 
| render timechart

Replace metric names with the following to create a chart of memory utilization:

let capacityCounterName = 'memoryCapacityBytes';
let usageCounterName = 'memoryRssBytes';

If you want to filter to a cluster, use this in place of comment in the query above:

| where ClusterName == '<my-cluster-name>'

Hope this is going to be a good start for your dashboard... As you explore the queries and tables available in Log Analytics with info on your cluster, you'll find much useful data...